This application is based on Japanese Patent Application No. 2000-176278 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a head-mounted display device and an eyepiece optical system suitable for use in said head-mounted display device which projects a two-dimensional image displayed on a display panel such as a liquid crystal display element onto the eye of an observer who perceives an enlarged virtual image.
2. Description of the Related Art
Conventionally, head-mounted display devices are equipped with a closed frame unit, an eyepiece optical system, and a mounting member (band, etc.) by which it may be mounted onto the user""s head. This type of head-mounted display device is mounted on the user""s head so that the eyepiece optical system is aligned with the user""s eyes, such that by looking inside the frame unit at the eyepiece optical system, a video image, television broadcast image or game image may be observed. When this image viewing device is used, the user may concentrate on the image and obtain a feeling of realism as if he himself were inside the image.
Conventionally, such head-mounted display devices include eyepiece optical systems having a so-called pancake structure wherein a planar two-dimensional projection image is enlarged using a reflective-transparent surface, and the enlarged image is viewed. For example, Japanese Laid-Open Patent Application No. 8-110492 discloses a structure comprising a partial optical system having at least two semi-transparent surfaces arranged so as to at least transmit one light ray and at least reflect one light ray, and a refractive optical element having optical power.
Furthermore, Japanese Laid-Open Patent Application No. 8-327940 discloses a structure which renders the device thin, compact and lightweight by providing a reflective-refractive element having a semi-transparent mirror coating and a circularly-polarized-light-selective semi-transparent mirror arranged sequentially from the ray entrance side, such that when an incident ray is a specific circularly-polarized ray, the circularly-polarized-light-selective semi-transparent mirror selectively reflects and transmits the incident ray by polarization, the optical power (magnification) of the refractive system is increased, and the field angle is enlarged by the incident light passing one-way between the reflective-refractive element and the selective semi-transparent mirror.
On the other hand, in order to realize an eyepiece optical system having less distortion and a thinner form-factor than a conventional co-axial type refractive optical system, it is desirable to examine the lens material and position of aspherical surfaces and spherical surfaces, aspects which are not mentioned in the conventional art.
An object of the present invention is to overcome these and other shortcomings of the prior art designs.
Another object of the present invention is to provide a head-mounted display device having an improved eyepiece optical system.
Another object of the present invention is to provide an eyepiece optical system capable of displaying a high quality virtual image which is thinner and has a shorter total length than conventional systems.
These objects are attained by a head-mounted display device comprising an eyepiece optical system which enlarges and displays a projection image displayed on a two-dimensional display element onto the eye of an observer, said eyepiece optical system comprising sequentially from an observer""s eye:
an aspherical resin lens having a first surface which is aspherical and a second surface which is approximately planar;
a spherical glass lens having a first surface which is concave; and
a polarization-conversion element for converting the projection light from the two-dimensional element to polarized light disposed between the spherical-surface glass lens and the two-dimensional display element;
wherein the second surface of the aspherical resin lens is provided with a circularly-polarized-light-selective reflecting-transmitting surface for selectively reflecting and transmitting projection image light from the two-dimensional display element depending on the rotation direction of the circularly-polarized rays, and the first surface of the spherical glass lens is provided with a semi-transparent mirror surface.
These objects are further attained by a head-mounted display device comprising an eyepiece optical system which enlarges and displays a projection image displayed on a two-dimensional display element onto an eye of an observer, said eyepiece optical system comprising sequentially from the observer""s eye:
an aspherical resin lens having a first surface which is aspherical and a second surface which is approximately planar;
a spherical glass lens having a first surface which is concave and a second surface which is convex; and
a polarization-conversion element for converting the projection light from the two-dimensional element to polarized light disposed between the spherical glass lens and the two-dimensional display element;
wherein the second surface of the aspherical resin lens is provided with a circularly-polarized-light-selective reflecting-transmitting surface for selectively reflecting and transmitting projection image light from the two-dimensional display element depending on the rotation direction of the circularly-polarized rays, and either the first surface or the second surface of the spherical glass lens is provided with a semi-transparent mirror surface.
The circularly-polarized-light-selective reflecting-transmitting surface is desirably formed of cholesteric liquid crystal. It is further desirable that the circularly-polarized-light-selective reflecting-transmitting surface comprises a xc2xc wavelength plate and a reflective-type polarizing plate.
It is also desirable that the polarization-conversion element comprises a polarizing plate and a xc2xc wavelength plate. The two-dimensional display element is desirably a liquid crystal panel, and the polarization-conversion element is desirable a xc2xc wavelength plate.